Painting an Aluminium Chassis
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Good Morning Mr. K Brown -- THANK YOU. I appreciate the clarification between hammered and wrinkle paint. The images you posted are helpful and illustrate the difference.
Well ... um ... er ... the manufacturer calls it "hammered."
I use Krylon Hammered Bronze which turns out very dark grey, almost, but not fully black. I prefer that to actual hammered black because it has more metalic bits and has more curb appeal. I agree with your and others' comments about how to handle, apply and harden the different types of paint.
I maintain, however, the hammered paint I use at least minimizes, and does not reveal, scratches and imperfections as easily as gloss or semi-gloss enamel paint. I seems easier to bake and harden with my cold water process. Smoother, glossy finish paint does not always turn out as well - at least it seems more fussy (in my experience.) So, while it may scratch just as easy, I believe it does not show the scratches as much as a smoother, glossier finish.
CAVEAT -- It appears I heat my pieces hotter than others indicate in their comments. Nevertheless, one must be careful to avoid overheating the piece, which sometimes reactivates and "melts" the paint to a point where it runs and drips, or (worse) boils and bubbles, which ruins an otherwise even applcition. As with so many things in life, one can have too much of a good thing!
DISCLAIMER -- nothing in my comments should be construed as contradicting what others have said. I am a mere amateur hobbyist and not a qualified chemical engineer, so I only speak from limited personal experience and satisfied consumer of $7 rattle can spray paint from the hardware store. I would LOVE to have my gear powder coated or painted by a commercial outfit ! Sadly, I have too many projects and not enough play dough in the budget.
Happy trails y'all. James
You need dry lint free cloths to finish with the IPA - no oil residue or you’ll get fisheyes in the paint. Jump through the grades of Scotchbrite and you’ll get a really good grippy surface to take paint. Just make sure the finish coat you want to use is either self priming or if it needs an etch primer to be applied first.
FWIW, the best self-etching primer I've ever used is SEM brand, which for decades has been my go-to on aluminum and stainless steel. It comes in black, gray and green, covers extremely well with one light coat, and while the fumes are kinda rough they're not as bad as some. The only caveat is that it's quite expensive. If you can get it in your country, it's some really good stuff. Mar-Hyde is also excellent, but even more expensive, and the fumes will carry you off into a land of flowers, unicorns and pretty colors.
Choice of primer color is also important as the primer affects the shade and hue of the finish coat. Paint is not opaque and the primer shows through as a color cast to the finish coat. So I use black primer for black, dark blue and dark charcoal, grey or white for white and light blue, grey for light red or black for dark red, green for any shade of green or blue/green, white for yellow and so on.
if you aint doing powder coating go for engine paint in a rattle can. aluminium can regect most paints rapidly
Wrinkle or hammered paints are actually two paints mixed together with different drying time.
When the faster one dry first, it pulls the second one causing the wrinkle finish.
k brown
Well-known member
You can use any paint on aluminum; just use a primer made for aluminum first.
For a really nice gloss or satin finish I use automotive paint - etch primer for the surface first coat, then 2 or more coats of base-coat colour and finally 2 or more coats of clear coat - choice of flat, satin or gloss. For aluminium chassis on tube amps the gloss looks superb. In the workshop I worked at doing luxury Supercars, when painting after the fast repairs for same day delivery, the paint coats were done “wet on wet” - base-coats first and then and clear coats straight over the top while the base-coat is wet - this provides much better adhesion of clear to the base-coat underneath - this is good for hot sunny environments where clear coats can delaminate - tube amp chassis can get warm for long periods of time. The trick is to use a mist coat to start whether doing normal drying between coats or wet on wet and build up the paint depth with subsequent coats - not heavy coats as they will run 
! This is the opposite of applying hammer or wrinkle finish paint where you need the heavy build up single coat for the hammer to work and the depth of paint for a good wrinkle finish.
! This is the opposite of applying hammer or wrinkle finish paint where you need the heavy build up single coat for the hammer to work and the depth of paint for a good wrinkle finish.Gratuitous Sidebar -
When I am in a hurry, or get impatient (which is often) - I use Rust-Oleum flat black backyard grill spray paint. It dries to the touch for handling in less than 15 minutes - especially if I hasten the process with a hot air gun. It is very hard and durable if allowed to cure overnight - especially if I do my heat gun-cold water treatment.
NOT a pretty finish, but fast and really hard and backyard grill paint definitely TAKES THE HEAT of a hot chassis!
Not necessarily recommended for pretty results. Just another method that works for those in a hurry wanting a quick, durable and heat-resistant finish. James
When I am in a hurry, or get impatient (which is often) - I use Rust-Oleum flat black backyard grill spray paint. It dries to the touch for handling in less than 15 minutes - especially if I hasten the process with a hot air gun. It is very hard and durable if allowed to cure overnight - especially if I do my heat gun-cold water treatment.
NOT a pretty finish, but fast and really hard and backyard grill paint definitely TAKES THE HEAT of a hot chassis!
Not necessarily recommended for pretty results. Just another method that works for those in a hurry wanting a quick, durable and heat-resistant finish. James
k brown
Well-known member
This works on aluminum without primer?Gratuitous Sidebar -
When I am in a hurry, or get impatient (which is often) - I use Rust-Oleum flat black backyard grill spray paint. It dries to the touch for handling in less than 15 minutes - especially if I hasten the process with a hot air gun. It is very hard and durable if allowed to cure overnight - especially if I do my heat gun-cold water treatment.
NOT a pretty finish, but fast and really hard and backyard grill paint definitely TAKES THE HEAT of a hot chassis!
Not necessarily recommended for pretty results. Just another method that works for those in a hurry wanting a quick, durable and heat-resistant finish. James
k brown
Well-known member
I think the Krylon marketing dpt. was 'hammered' when they named it . . .Good Morning Mr. K Brown -- THANK YOU. I appreciate the clarification between hammered and wrinkle paint. The images you posted are helpful and illustrate the difference.
Well ... um ... er ... the manufacturer calls it "hammered."
I use Krylon Hammered Bronze which turns out very dark grey, almost, but not fully black. I prefer that to actual hammered black because it has more metalic bits and has more curb appeal. I agree with your and others' comments about how to handle, apply and harden the different types of paint.
I maintain, however, the hammered paint I use at least minimizes, and does not reveal, scratches and imperfections as easily as gloss or semi-gloss enamel paint. I seems easier to bake and harden with my cold water process. Smoother, glossy finish paint does not always turn out as well - at least it seems more fussy (in my experience.) So, while it may scratch just as easy, I believe it does not show the scratches as much as a smoother, glossier finish.
CAVEAT -- It appears I heat my pieces hotter than others indicate in their comments. Nevertheless, one must be careful to avoid overheating the piece, which sometimes reactivates and "melts" the paint to a point where it runs and drips, or (worse) boils and bubbles, which ruins an otherwise even applcition. As with so many things in life, one can have too much of a good thing!
DISCLAIMER -- nothing in my comments should be construed as contradicting what others have said. I am a mere amateur hobbyist and not a qualified chemical engineer, so I only speak from limited personal experience and satisfied consumer of $7 rattle can spray paint from the hardware store. I would LOVE to have my gear powder coated or painted by a commercial outfit ! Sadly, I have too many projects and not enough play dough in the budget.
Happy trails y'all. James
View attachment 116361
Well... um ... er ... It is supposed to go directly on BBQ grills, which are often made of cast aluminum. Unfortunately, I don't have a can in stock, so I cannot check its actual instruction set.
and yet ... AHEM ... Further research yields a product data sheet which includes this curious tidbit:
Incompatibility: ... Product slowly corrodes copper, aluminum, zinc, and galvanized surfaces.
I find this curious because it is a rust inhibiting product which, apparently, slowly corrodes what it is supposed to protect ... so shoot, you be the judge. It has always worked for me, and yet this little tidbit raises doubts. Go figure. James
k brown
Well-known member
Rust is oxidised iron or steel - different corrsion process than aluminum:
https://www.kloecknermetals.com/blog/aluminum-oxidation-is-aluminum-corrosion-resistant/
https://www.kloecknermetals.com/blog/aluminum-oxidation-is-aluminum-corrosion-resistant/
Thanks for the link. I am learning something all the time. Thanks. James
scott2000
Well-known member
Interesting....
It almost seems like coating the oxidation could be preferred to removing it then coating if it's already happened?
Etch primers break down the aluminium oxide layer which if left in place when using ordinary paints, the paint will flake off. This primer also works for other ferrous and non-ferrous metals and also fibreglass gelcoat. Aluminium oxidises almost immediately after sanding, polishing or grinding.
The active ingredient in etch primer both single and 2 pack is an acid - this acid loses strength in less than 18 months so shelf life of single pack etch primers is limited, 2 pack lasts longer around 36 months (or until you mix the paint!) - check the batch date. Contrary to some beliefs that etch primer keeps eating the metal, the acid itself neutralises at the surface of the metal, it’s usually phosphoric acid, and once the 24hr cure time has elapsed the etchant has no detrimental effect on following paint coats or the metal underneath. The primer if multipurpose usually contains zinc phosphate as well for rustproofing metals like iron and steel. Salt air is one of the biggest destroyers of metalwork along with galvanic action occurring with dissimilar metals and electrical current flow.
With oxidation the junction between the metals becomes highly resistive or non conducting. In aluminium chassis with current carrying ground posts the contact between the ground bolt and the chassis will break down with time, with no current it takes a lot longer - signal grounds should not use the chassis as a conductor for signal current, nor should DC power. Steel wheel bolts on alloy wheels can lock to the alloy seat and freeze in place due to heat and impurities in road surface water - stainless steel seems to be ok. I always use stainless bolts and washers for chassis ground connection - the zinc galvanised ones seem to become non conductive with aluminium after a fairly short time, the bright nickel are better, stainless steel seems to be the slowest to react and as long as there is no moisture and no electrical current flowing it lasts a long time. I’ve seem metal salt “fur” growing from bolted junctions to aluminium framework that have been used as current carrying connections in high salt air environments like sailing boats.
The active ingredient in etch primer both single and 2 pack is an acid - this acid loses strength in less than 18 months so shelf life of single pack etch primers is limited, 2 pack lasts longer around 36 months (or until you mix the paint!) - check the batch date. Contrary to some beliefs that etch primer keeps eating the metal, the acid itself neutralises at the surface of the metal, it’s usually phosphoric acid, and once the 24hr cure time has elapsed the etchant has no detrimental effect on following paint coats or the metal underneath. The primer if multipurpose usually contains zinc phosphate as well for rustproofing metals like iron and steel. Salt air is one of the biggest destroyers of metalwork along with galvanic action occurring with dissimilar metals and electrical current flow.
With oxidation the junction between the metals becomes highly resistive or non conducting. In aluminium chassis with current carrying ground posts the contact between the ground bolt and the chassis will break down with time, with no current it takes a lot longer - signal grounds should not use the chassis as a conductor for signal current, nor should DC power. Steel wheel bolts on alloy wheels can lock to the alloy seat and freeze in place due to heat and impurities in road surface water - stainless steel seems to be ok. I always use stainless bolts and washers for chassis ground connection - the zinc galvanised ones seem to become non conductive with aluminium after a fairly short time, the bright nickel are better, stainless steel seems to be the slowest to react and as long as there is no moisture and no electrical current flowing it lasts a long time. I’ve seem metal salt “fur” growing from bolted junctions to aluminium framework that have been used as current carrying connections in high salt air environments like sailing boats.
scott2000
Well-known member
So if paint is already flaking, with oxidation showing in the exposed areas, it's better to strip, then etch and repaint? Maybe there wasn't an etch primer used initially? I see it all the time on cheap and not so cheap patio furniture
Is this 1 pack/2pack referring to1k and 2k products?
wow... something tells me there is possibly some stale stuff lying around on shelves
So what would be the best process to deal with a painted piece of aluminum that lives right on the beach? That is bubbling, flaking and has oxidation in the exposed sections Like a permanent piece of furniture that can't be brought inside? If there's a cure time for the primer, I'm guessing the constant bombardment of salt air comes into play.
What about bolts? I've literally stripped bare, etch primed and painted, albeit withing a few hours of each other and, the next morning there is rust that almost seems like it's coming from the coating itself but idk....
My neighbor who deals with fasteners said that the stainless steel bolts that Tapcon makes for example aren't high grade stainless because it makes them weaker iirc, so they will rust in fairly short order... and he really couldn't offer advice in an extreme salt environment
The furniture doesn’t necessarily have to be cheap - wear and dings let the salt through. Gaps in coating or points of contact of fasteners which will tear the paint will be corrosion start points.
The only way, if paint is flaking off, is to strip and use marine grade etch primer and paints. 2K is preferable and coating must be 100% - no gaps or thin coats - paint is slightly porous and a good sealing inhibiting etch primer should be used and check the batch date or use-by date. The primer must fully cure before top coats. Rust will leach through paint if the primer has not sealed and protected the surface fully, also if it’s (the etch primer) past the use-by date.
Powder coating is the simplest commercial solution for metals near salt air, but you can’t DIY it, you need to buy products made that way with the powder coating already done.
Anodizing is another method but once again not for DIY unless you have a handy garden furniture sized tub of sulphuric acid and a 100VDC 36A or more power supply lying around - you need to buy it already done.
1 and 2 pack are 1K 2K - 2K have a separate hardener and once combined form a tougher more durable finish.
Marine fasteners are usually best to use - these will be 316L or better, Nitronic 60 best for immersion but may be difficult to find.
Normal steel bolts need an etch primer with heavy zinc phosphate content and must fully cure before final coating - where the threads meet the paint will strip anyway as will the connecting face of the underside of the bolt head to the bolted surface. Best to use stainless and not paint as stainless needs oxygen to self repair. There are also grades of stainless used in surgical implants but we don’t need to go there - the bolts and nuts would likely cost more than a set of patio furniture.
https://www.anzor.com.au/blog/painting-stainless-steel
Edit: you can buy hard anodized nuts and bolts in various colours. Good for decorative outdoor stuff. The surface of these is non conductive so can be a go for audio gear chassis ground post providing the ground wire lug directly contacts the chassis (or via a star washer which will bite the surface of the chassis and lug - some vintage audio gear and synths I have serviced have star washer lugs for aluminium chassis grounds).
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scott2000
Well-known member
What about the non-stop bombardment of salt air while it's curing, top coats etc? Think aluminum railing .... Protecting in an environment with minimum 18mph wind with 25 to 30 gusts constantly would be nightmarish
does it matter?
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